Stacked Semiconductor Device Assembly

ABSTRACT

The semiconductor device system includes multiple stacked substantially identical semiconductor devices each including a first side and an opposing second side. First and second pads are disposed at the first side of the semiconductor device, while third and fourth pads are disposed at the second side of the semiconductor device. First interface circuit is electrically coupled to the first pad and the third pad, while second interface circuit is electrically coupled to the second pad and the fourth pad. The second interface circuit is separate and distinct from the first interface circuit. At least one first semiconductor device of the multiple semiconductor devices is offset from other of the multiple semiconductor devices such that the fourth pad on the first semiconductor device is aligned with, and electrically connected to, the first pad on an adjacent one of the multiple semiconductor devices. In some embodiments, the first pad is associated with a first capacitance, while the second pad is associated with a second capacitance that is smaller than the first capacitance.

TECHNICAL FIELD

The embodiments disclosed herein relate to semiconductor devices, and inparticular to a stacked semiconductor device assembly with at least oneof the semiconductor devices offset from the remainder of thesemiconductor devices.

BACKGROUND

As computer systems evolve, so does the demand for increased memory forsuch systems. To increase memory density, some memory packages consistof several integrated circuit (IC) dies stacked one on top of the other.These stacked multi-die packages increase the capacity of each memorydevice without requiring additional space on the underlying circuitboard or memory module. Furthermore, Thru-Silicon Via (TSV) technologyis emerging as a popular solution for enabling the largest number ofdie-to-die interconnect in multi-die packages.

There are, however, a number of drawbacks associated with stackedmulti-die packages, especially when TSV's are used as theinterconnection means. For one, it is often desirable from amanufacturing cost perspective that all of the dies in the stack arederived from the same mask set, i.e., that all of the dies in a stackare substantially identical. When identical dies are stacked in apackage and interconnected by TSV's, however, it is often difficult toselectively enable different modes of operation to a subset of the dieswithin the stack. For example, if the TSV's interconnect the stackeddevices at the input/output (“IO”) pad of each die, there will be alarge aggregation of capacitance at that point. In particular, each diecontributes capacitance associated with that die's IO pad metal, IOdevice loading, IO devices, and electrostatic discharge (ESD) deviceloading. With such a large aggregated capacitance, the stack of diewould become severely limited in operational speed compared to one ofthe die on its own.

In other stacked multi-die packages, the TSV's may interconnect thestacked dies internally, “behind” the IO system, using some sort ofmulti-drop data bus topology. In these packages, one of the dies acts asthe “bus master”, while others act as “slave devices.” If the dies aresubstantially identical, it is difficult to designate one of the devicesas the “bus master” without utilizing bus-multiplexing circuitry that isnon-optimal from a cost and performance perspective.

In yet other stacked multi-die packages, it may be possible to add oneor more manufacturing steps to modify some features or connections onsome of the devices to facilitate die stacking Performing suchmodifications, however, adds significant manufacturing and inventorycontrol costs. As a result, the complexity and manufacturing andassembly costs for the stacked semiconductor device assembly areincreased substantially.

As such, it would be highly desirable to provide a stacked die assemblythat utilizes substantially identical dies and that enables selectivemodes of operation for at least a subset of the dies in the stack.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the disclosure herein, reference should bemade to the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a plan view of an exemplary stacked semiconductor deviceassembly;

FIG. 1B is a cross sectional view of the stacked semiconductor deviceassembly shown in FIG. 1A, as viewed along line 1B-1B′ of FIG. 1A;

FIG. 2A is a schematic diagram of a semiconductor device in the stackedsemiconductor device assembly shown in FIGS. 1A and 1B;

FIG. 2B is a schematic circuit diagram 210 of one embodiment of aportion of the semiconductor device shown in FIG. 2A;

FIG. 2C is a schematic circuit diagram of a portion of a stackedsemiconductor die assembly using devices like the one shown in FIG. 2B;

FIG. 2D is a schematic diagram of another stacked semiconductor dieassembly with mode enable circuitry;

FIG. 2E is a schematic circuit diagram of the mode enable circuitry ofFIG. 2D;

FIG. 3 is a schematic cross-sectional side view (cross-hatching removedfor clarity) of another exemplary stacked semiconductor device assembly;

FIG. 4 is a schematic cross-sectional side view (cross-hatching removedfor clarity) of another exemplary stacked semiconductor device assembly;

FIG. 5 is a plan view of another exemplary stacked semiconductor deviceassembly; and

FIG. 6 is a schematic of a computer system using a stacked memorysemiconductor device assembly.

Like reference numerals refer to the same or similar componentsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following describes a number of exemplary assemblies that addressthe issues associated with multiple semiconductor devices being stackedtogether to form a semiconductor packaging assembly (or package), inwhich at least one semiconductor device in the stack performs differentfunctions or electrical operations as compared to the other devices inthe stack. Stated differently, an interface semiconductor device, whilebeing substantially identical to the other devices in the assembly,performs different functions from those performed by the othersemiconductor devices in the stack; or the interface semiconductordevice operates in a different mode of operation from the mode ofoperation of the other devices. In one embodiment, the interface deviceconnects to circuitry external to the stacked semiconductor deviceassembly, and is conveniently placed at the bottom of the stack ofsemiconductor devices in the assembly. For example, the interfacesemiconductor device may include all of the active external-IO circuitry(such as the ESD circuitry), while the remainder of the semiconductordevice in the stack have lower-power “intra-stack” IO circuitry. Inanother example, the interface device may perform master read/writeoperations while the other devices perform slave read/write operations.

According to some embodiments there is provided a semiconductor deviceassembly that includes multiple stacked substantially identicalsemiconductor devices each including a first side and an opposing secondside. First and second pads are disposed at the first side of thesemiconductor device, while third and fourth pads are disposed at thesecond side of the semiconductor device. First interface circuit iselectrically coupled to the first pad and the third pad, while secondinterface circuit is electrically coupled to the second pad and thefourth pad. The second interface circuit is separate and distinct fromthe first interface circuit. At least one first semiconductor device ofthe multiple semiconductor devices is offset from other of the multiplesemiconductor devices such that the fourth pad on the firstsemiconductor device is aligned with, and electrically connected to, thefirst pad on an adjacent one of the multiple semiconductor devices. Thesemiconductor device assembly may be a multi-die memory chip, such as amulti-die DRAM chip, which may then be attached to a memory module, suchas a DRAM memory module

In some embodiments, the first side and the second side aresubstantially planar and parallel to one another. Also in someembodiments, the first and third pads are electrically coupled to eachother by a first via through the semiconductor device, and the secondand fourth pads are electrically coupled to each other by a second viathrough the semiconductor device. These vias may be through-silicon-vias(TSVs). In these embodiments, the first and third pads are aligned withone another along an axis substantially perpendicular to the first andsecond sides of the semiconductor device, and the second and fourth padsare aligned with one another along an axis substantially perpendicularto the first and second sides of the semiconductor device.

In use, and in the context of the semiconductor device being a memorydevice (such as a DRAM, an SRAM, a Flash memory IC, or other types ofmemory chip), the semiconductor device communicates data over aninternal signal line to or from core interface circuit using either thefirst interface circuit or the second interface circuit depending onwhether the first and third pads, or the second and fourth pads, arecoupled to an external signal line. The core interface circuit mayinclude a data transmitter or a data receiver. The internal signal lineis either unidirectional or bidirectional.

In some embodiments, the first interface circuit and the secondinterface circuit have different capacitances, e.g., the first interfacecircuit includes electrostatic discharge (ESD) circuitry. In otherembodiments, the first interface circuit is a read channel master andthe second interface circuit is a read channel slave, e.g., the firstinterface circuit is a write channel master and the second interfacecircuit is a write channel slave.

According to some embodiments there is provided a method for selectivelyenabling a mode of semiconductor device in a stacked semiconductordevice assembly. Multiple semiconductor devices that are substantiallyidentical to one another are provided, as described above. The multiplesemiconductor devices are then stacked one on top of the other. Finally,at least a first semiconductor device of the multiple semiconductordevices is spatially offset from the remainder of the multiplesemiconductor devices such that the fourth pad on the firstsemiconductor device is aligned with, and electrically connected to, thefirst pad on an adjacent one of the multiple semiconductor devices.

Finally, according to some embodiments there is provided a computingassembly that includes a bus; a processor coupled to the bus;communication circuitry coupled to the bus; semiconductor devices, asdescribed above, forming multi-die memory chips that are coupled to thebus, where the multi-die memory chips include stacked semiconductors oneon top of the other, and spatially offsetting at least a firstsemiconductor device of the multiple semiconductor devices from theremainder of the multiple semiconductor devices such that the fourth padon the first semiconductor device is aligned with, and electricallyconnected to, the first pad on an adjacent one of the multiplesemiconductor devices.

These embodiments provide a stacked semiconductor device assembly thatallows for one or more semiconductor devices in the stack of identicalsemiconductor devices to have a different mode of operation to theremainder of the semiconductor devices in the stack.

FIG. 1A is a plan view of an exemplary stacked semiconductor deviceassembly 100, while FIG. 1B is a cross sectional view of the stackedsemiconductor device assembly shown in FIG. 1A, as viewed along line1B-1B′ of FIG. 1A. The stacked semiconductor device assembly includes atleast two semiconductor devices 102(1) and 102(2). In some embodiments,the semiconductor device is a die, i.e., an unpackaged bare integratedcircuit or chip. In some of these embodiments, the semiconductor deviceis a memory die (e.g., DRAM, SRAM, Flash, RRAM, FeRAM, MRAM, etc.). Inother embodiments, the semiconductor device is any packaged orunpackaged integrated circuit or the like. The stacked semiconductordevice assembly 100 is particularly well suited to memory because of theneeds for multiple substantially identical die that, in aggregate,satisfy the ever increasing demands on memory capacity and density.

The semiconductor devices 102(1), 102(2) are substantially identical toone another, so they can be fabricated using a same or substantiallysame set of semiconductor fabrication process steps. Each of thesemiconductor devices 102(1), 102(2) has a substantially planar firstside 106(1), 106(2) and an opposing substantially planar second side108(1), 108(2). Each semiconductor device 102(1), 102(2) also includesactive circuitry 110(1), 110(2), including interface circuit, modalselect circuitry, core interface circuit, a core, and/or the like, asdescribed below. In some embodiments, the active circuitry is formednear or at the first side 106(1), 106(2) of each semiconductor device.

Each of the semiconductor devices 102(1), 102(2) has a first group ofconnection pads 112(1), 112(2); a second group of connection pads114(1), 114(2); a third group of connection pads 120(1), 120(2); and afourth group of connection pads 122(1), 122(2). The connection pads on asemiconductor device are for connection circuits formed on the device tocircuits external to the device. In one example, the connection pad maybe input/output (I/O) pads for connection to circuits external theassembly (e.g., other chips in the computer system). In another example,the connection pads may be contact pads for connecting to one or moreintra-assembly buses. The connection pads may be of any suitable shape,such as square, round or the like. In some embodiments each group ofconnection pads is a stripe of connection pads that extend substantiallyacross a respective side of each semiconductor device, i.e., each stripemay form a column (or row, depending on orientation) across a side ofeach semiconductor device. In some embodiments, each group of connectionpads is located near the middle of a respective side of a semiconductordevice, however, in other embodiments, the connection pads may belocated near an edge or anywhere else on the semiconductor device. Inother embodiments, each of the groups of connection pads may includemultiple stripes of connection pads, e.g., each group includes twostripes of connection pads. In some embodiments, first group ofconnection pads 112(1), 112(2) and the second group of connection pads114(1), 114(2) are disposed at the first surface 106(1), 106(2) of eachof the respective semiconductor devices. Similarly, in some embodiments,the third group of connection pads 120(1), 120 (2) and the fourth groupof connection pads 122(1), 122 (2) are disposed at the second surface108(1), 108(2) of each of the respective semiconductor devices.

In some embodiments, each connection pad of the first group ofconnection pads 112 is aligned with and electrically connected to acorresponding connection pad of the third group of connection pads 120.Similarly, each connection pad of the second group of connection pads114 is aligned with and electrically connected to a correspondingconnection pad of the fourth group of connection pads 122. By alignedwith it is meant that the connection pads are aligned along axes thatare substantially perpendicular to both the first side 106 and thesecond side 108 of each semiconductor device (e.g., along axes parallelto a Z-axis perpendicular to both of the X and Y axes of FIG. 5). Insome embodiments, the electrical connections between the connection padsof the first group of connection pads 112 and the connection pads of thethird group of connection pads 120 is through a series of vias, two ofwhich are shown by reference numerals 116(1), 116(2) (FIG. 1B) thatextend through each semiconductor device from the connection pads at thefirst side 106 to the connection pads at the second side 108 of each ofthe respective semiconductor devices. Similarly, the electricalconnections between the connection pads of the second group ofconnection pads 114 and the connection pads of the fourth group ofconnection pads 122 is also through a series of vias, one of which areshown by reference numerals 118(2) (FIG. 1B) that extend through eachsemiconductor device from the connection pads at the first side 106(1),106(2) to the connection pads at the second side 108(1), 108(2) of eachof the respective semiconductor devices. In other words, in someembodiments, each connection pad on the first side is connected to acorresponding pad at the second side through a single via.

In some embodiments, each of the vias may be referred to as a throughchip via (“TCV”) or through silicon via (“TSV”). Also in someembodiments, the vias 116 and 118 are substantially aligned with theirrespective pads along the axes defined above. The vias may be formed byany suitable technique, such as by thinning a wafer that contains a deepmetal via formed during semiconductor processing, or by electroplatingthrough-holes formed by laser drilling subsequent to semiconductormanufacturing, or by other techniques well known in the industry. Insome embodiments (not shown), the vias are filled with a conductivematerial. In other embodiments, the electrical connections between theconnection pads on the first side 106(1), 106(2) and the connection padson the second side 108(1), 108(2) can be made through any other suitableelectrical connections including traces, redistribution layers,different types and sizes of vias, leads, tape, wires, or anycombination of the aforementioned.

As will be explained in more detail below, during assembly, the secondsemiconductor device 102(2) (typically an upper semiconductor device) isstacked adjacent to the first semiconductor device 102(1) (typically abottommost semiconductor device) such that the second group ofconnection pads 114(2) of the second semiconductor device 102(2) isadjacent to and aligned with the third group of connection pads 120(1)of the first semiconductor device 102(1). Stated differently, the secondsemiconductor device is offset (stepped or moved along the X and/or Yaxes of FIG. 5) from the first semiconductor device by a distance equalto an integer multiple of the pitch between the respective groups ofconnection pads (120 and 122, and/or 112 and 114) on each side of eachsemiconductor device. FIG. 2B illustrates an offset distance where theinteger multiple is “1”, but other values may be used. Each of theconnection pads of the second group of connection pads 114(2) of thesecond semiconductor device 102(2) is then electrically connected to acorresponding connection pad of the third group of connection pads120(1) of the first semiconductor device 102(1). These electricalconnections are made by any suitable means, such as by a solder reflowprocess, as depicted by solder contact 128. Thermosonic flip chipbonding, thermocompression bonding, or other techniques common inmulti-die bonding may also be used. In some embodiments, theseelectrical connections are made through “solder bumps”, “micro-bumps”,or “C4 bumps” at each connection pad.

In some embodiments, the first semiconductor device 102(1) iselectrically and/or mechanically connected to a package substrate 124,such as is used in flip-chip (FC) packaging. The FC package substrate isthen usually electrically coupled to a printed circuit board (PCB) via aball-grid array (BGA) connection technology (not shown). In particular,the connection pads of the first group of connection pads 112(1) on thefirst semiconductor device 102(1) are electrically connected to thesubstrate 124. In some embodiments, these electrical connections aremade by any suitable means, such as by soldering connection pads to oneanother, as depicted by reference numeral 126. In some embodiments,these electrical connections are made through “solder bumps” or “C4bumps” at each connection pad.

Once assembled, the stacked semiconductor device assembly 100 allowselectrical signals to be communicated between electrical connections onthe substrate 124 and those on the second semiconductor device 102(2)through the first semiconductor device 102(1). Here, the firstsemiconductor device 102(1) acts as the primary interface semiconductordevice between the substrate 124 and the remainder of the semiconductordevices (here semiconductor device 102(2)) in the stacked semiconductordevice assembly 100, and it may have active interface circuitry (e.g.,ESD protection circuitry) that is different from the remainder of thesemiconductor devices in the stack.

FIG. 2A is a schematic diagram of a semiconductor device 102 in thestacked semiconductor device assembly shown in FIGS. 1A and 1B. Thesemiconductor device 102 shows a first connection pad 112 from the firstgroup of connection pads 112(1), 112(2) of FIGS. 1A and 1B, and a secondconnection pad 114 from the second group of connection pads 114(1),114(2) of FIGS. 1A and 1B.

The first connection pad 112 is electrically connected to firstinterface circuit 220, and the second connection pad 114 is electricallyconnected to second interface circuit 222.

In some embodiments, the first interface circuit 220 and the secondinterface circuit 222 electrically connect to a single signal path 221made of, for example, a signal conducting line. This signal path 221 maybe unidirectional or bidirectional. The signal line 221 is in turnelectrically connected to core interface circuit 212, which may includea serializer or deserializer, and which may either generate and transmitsignals to the signal line 221, or receive signals from the signal line221. The core interface circuit 212 electrically connects to the core111 (such as memory cells or memory banks) through multiple connections.The core 111 and core interface circuit 212, are well understood in theart.

The ability to access the core 111 via either the first connection pads112 or the second connection pads 114 provides the designer of thestacked semiconductor device assembly the ability to have a particularsemiconductor device in the stack operate in a different mode from theremainder of the semiconductor devices in the stacked semiconductorassembly, i.e., perform functional or electrical operations differentlyto other semiconductor devices in the stacked semiconductor assembly.The ability to have different modes of operation within a stackedsemiconductor assembly is provided despite the stacked semiconductorassembly containing substantially identical semiconductor devices.

FIG. 2B is a schematic circuit diagram 210 of one embodiment of aportion of the semiconductor device shown in FIG. 2A. In thisembodiment, interface circuits 220 and 222 include output drivers 226and 224, respectively, for transmitting signals from the semiconductordevice. One skilled in the art, however, will appreciate that a similarcircuit may be included in interface circuits 226 or 224 for receivingsignals into the semiconductor device. The first connection pad 112connects to the first interface circuit 220, while the second connectionpad 114 connects to the second interface circuit 222. The firstinterface circuit 220 includes first driver 226 and ESD circuitry 228.The second interface circuit includes second driver 224. The first andsecond drivers 226, 224, respectively, electrically connect to thesingle signal line 221 that is in turn connected to a data generator232, which forms part of the core interface circuit 212. The first andsecond driver circuitry 226, 224, respectively, also electricallyconnects to modal select circuitry 234, which may or may not form partof the core interface circuit 212. The modal select circuitry enableseither the first driver 226 or the second driver 224. Suitable modalselect circuitry is described in relation to FIG. 2E. In otherembodiments, no modal select circuitry 234 is provided. In theseembodiments, the desired circuitry or mode is enabled (e.g., powered-up,connected to an enable signal, connected to an output pad, etc.) byvirtue of either making or not making a physical electrical connectionat the interface semiconductor device.

In some embodiments, such as the embodiment described above in relationto FIG. 2B, the first interface circuit 220 has a first capacitance(C+), and the second interface circuit 222 has a second capacitance (C−)that is lower than the first capacitance. In some embodiments, thesecapacitances are representative of the aggregated capacitances of theactive circuitry itself, the ESD circuitry 228, driver circuitry 224 or226, the pad metal, and all electrical connections, such as traces etc.,that are coupled to each of the connection pads 112 and 114. In use, themodal select circuitry can enable either the signal path through thefirst interface circuit 220 and the first connection pad 112, or thesignal path through the second interface circuit 222 and the secondconnection pad 114.

FIG. 2C is a schematic circuit diagram of a portion of a stackedsemiconductor die assembly using devices like the one shown in FIG. 2B.By offsetting a semiconductor device, as described in relation to FIGS.1A and 1B, and in some embodiments controlling the modal selectcircuitry 234, different semiconductor devices in the stackedsemiconductor assembly operate in different modes. An interfacesemiconductor device 102(1) is offset (see FIG. 1B) from the remainderof the device in the stacked semiconductor assembly, so that theconnection pad 112 and the interface circuit 220 is enabled. Theconnection pad 112 on the interface device 102(1) is connected to theconnection pads 114 on the remainder of the semiconductor devices102(2), 102(3), and 102(4) in the stacked semiconductor die assembly.The connections between the connection pads 112 and 114 may be throughvias and other connection pads as described above in relation to FIGS.1A and 1B. As the connection pad 112 and the first interface circuit 220is enabled on the interface semiconductor device 102(1) (and not thesecond connection pad 114 and second interface circuit 222), theinterface semiconductor device 102(2) operates in a different mode tothe remainder of the semiconductor devices in the stacked semiconductorassembly. For example, the interface semiconductor device has the driverconnected to ESD circuitry enabled, while the remainders of the devicesin the stacked semiconductor assembly do not. In embodiments where nomodal select circuitry 234 is provided, the first interface circuit 220is used if the signal path is through the first connection pad 112, andthe second interface circuit 222 is used if the signal path is throughthe second connection pad 114.

There are many advantages of the above described stacked semiconductorassembly. For example, as the higher capacitance is disabled for allexcept the interface device 102(1), the resulting capacitive loading onthe external interface is drastically reduced, and, therefore, theoverall performance of the stack is increased, as compared to anembodiment having identical semiconductor devices all having highcapacitance loading. The above described embodiment also eliminateshaving to downsize the ESD protection circuitry in each of thesemiconductor devices in the stack so that the overall aggregated ESDprotection of the stack is at a desired level. Downsizing the ESDprotection in each semiconductor device restricts the stack count to anumber or amount of semiconductor devices that have a collective ESDprotection amount. For example, if each semiconductor device has 500VHBM ESD tolerance, where the desired ESD protection amount of the stackis 2000V HBM, then no less than four semiconductor devices can be usedin the stack. Instead, in the above described embodiments, the ESDprotection circuitry is only enabled in the interface semiconductordevice 102(1), thereby eliminating: (i) having to downsize the ESDprotection circuitry in each of the semiconductor devices, and (ii) anyrestriction on the number of semiconductor devices that can be used inany one stacked semiconductor assembly. It should also not be overlookedthat the stacked semiconductor assemblies described herein all make useof substantially identical semiconductor devices. This drasticallyreduces the complexity and cost of manufacturing and assembling suchstacked semiconductor assemblies.

FIG. 2D is a schematic diagram of another stacked semiconductor deviceassembly 240 that includes a plurality of substantially identicalsemiconductor devices 236(1)-236(n), wherein the spatial offsettechnique is used to enable different modes of operation for thesubstantially identical semiconductor devices. Each of the semiconductordevices 236 includes a number of connection pads, including: a master-inconnection pad (M In), a master enable connection pad (or mode enable orselect connection pad, labeled “M/E”), a first master connection pad(M1), a second master connection pad (M2), a first slave connection pad(S1), and a second slave connection pad (S2). In some embodiments, themaster-in connection pad (M in), master enable connection pad (M/E),first master connection pad (M1), and first slave connection pad (S1)are disposed at a first side of each semiconductor device, while thesecond master connection pad (M2) and the second slave connection pad(S2) are disposed at the second side of the semiconductor device. Thefirst and the second sides are opposite to one another and may besubstantially planar. The first master connection pad (M1) is connectedto the second master connection pad (M2) through a via, such as a TSV.Similarly, the first slave connection pad (S2) is connected to thesecond slave connection pad (S2) through a via, such as a TSV.

In some embodiments, each semiconductor device 236 also includescircuitry, including: an I/O buffer 244 for receiving and bufferinginput signals received at the master-in connection pad (M In); a readand/or write channel master circuit 246; a read and/or write channelslave circuit 248; a core interface circuit 250; a core 252 (e.g., aDRAM memory core, a flash memory core, a processor array core, etc.);and/or a mode select circuit 234. In some embodiments, the mode selectcircuit is located at or near the first side of each semiconductordevice.

In some embodiments, the read and/or write channel master circuit 246 iselectrically connected to the I/O buffer 244; the mode select circuitry234; the first master connection pad (M1), which is in turn connected tothe second master connection pad (M2) through a TSV; and the read and/orwrite channel slave circuit 248. In these embodiments, the read and/orwrite channel slave circuit 248 is electrically connected to the readand/or write channel master circuit 246; the core interface circuit 250;the first slave connection pad (S1), which is in turn connected to thesecond slave connection pad (S2) through a TSV; and/or mode selectcircuitry 234. The core interface circuit 250 is connected to the core252.

In use, the first semiconductor device 236(1) can be spatially offsetfrom the remainder of the semiconductor devices in the stack, such thatthe second master connection pad (M2) of the first semiconductor device236 (1) is connected to and aligned with the first slave connection pad(S1) of the second semiconductor device 236(2) in the stack. As with theembodiment described in FIGS. 1A and 1B, the second master connectionpad (M2) is aligned with the first slave connection pad (S1) along anaxis that is substantially perpendicular to the opposing two sides ofthe semiconductor device (i.e., along an axis substantially parallel tothe Z-axis and substantially perpendicular to the X and Y axes of FIG.5).

While any suitable mode enable or select circuitry 234 may be used, FIG.2E demonstrates how a resistor to ground can provide the functionalityof one such suitable circuitry. The schematic 234 includes a multiplexer(Mux) connected to inputs associated with, for example, data path (0)and data path (1). In this embodiment, the first path (0) is the defaultmode, while the second mode (1) is the mode enabled if the M/E signal iselectrically attached to VDD.

In FIG. 2E, the select input of the Mux is connected to ground through aresistor. If the M/E signal pad is left unconnected, the resistor will“pull down” the select input to ground, thereby defaulting the Mux tothe first mode (0). A similar technique can be used to create a global“Slave Enable” for the entire die. On the other hand, if a VDDconnection is made to the master enable connection pad (M/E), the modeselect signal will driven to VDD, thereby selecting the Mux to thesecond mode (1). A similar technique can be used to create a global“Master Enable” for the entire die. In other embodiments, separate modeselect or enable circuitry may be provided for each of the read and/orwrite channel master circuit 246 (FIG. 2D) and the read and/or writechannel slave circuit 248 (FIG. 2D).

Returning to FIG. 2D, a VDD signal is attached to the master enableconnection pad (M/E) of the first semiconductor device 236(1) only,thereby enabling the read and/or write channel master circuit 246. Themaster enable connection pad (M/E) of the remainder of the semiconductordevices 236(2)-236(n) is not connected, thereby, enabling the defaultread and/or write channel slave circuit 248 on the remainder of thesemiconductor devices 236(2)-(n).

In use, write signals received on the master-in connection pad (M In)are received and pass through the I/O buffer 244 to the read and/orwrite channel master circuit 246. Typically, a read interface of mastercircuit 246 includes data receivers, while a write interface of mastercircuit 246 includes data transmitters. The signal then passes from theread and/or write channel master circuit 246 to both the first masterconnection pad (M1), through the TSV to the second master connection pad(M2) and to the first slave connection pad (S2) on the adjacentsemiconductor device. The signal also passes from the read and/or writechannel master circuit 246 to the read and/or write channel slavecircuit 248 of the same device, whereby it is passed onto the coreinterface circuit 250 and the core 252.

Write signals received at the second and subsequent semiconductordevices travel from the first slave connection pad (S1) to the secondslave connection pad (S2) through a TSV and onto subsequentsemiconductor devices in the stack. The signal also travels from thefirst slave connection pad (S1) of the second and subsequent devices236(2)-(n) to the read and/or write channel slave circuit 248. The readand/or write channel slave circuit 248 may include read and/or writeinterfaces (not shown). The read interface of slave circuit 248 includesdata transmitters, while the write interface of slave circuit 248includes data receivers. In one embodiment, duplicate read and/writeinterfaces or duplicate transmitters and/or receivers may be provided inslave circuit 248 to communicate data with the master circuit 246 on thesame device as the slave circuit 248 and the master circuit on anotherdevice, respectively. As shown in FIG. 2D, slave circuit 248 may alsouse the signal generated by select circuitry 234 to determine which ofits receivers and/or transmitters need to be activated (i.e., whetherit's interfacing with a master interface circuit 246 on the same die asitself or on another die in the stack). Finally, the signal travels fromthe read and/or write channel slave circuit 248 to the core interfacecircuit 250 and the core 252. Accordingly, by spatially offsetting thefirst of the substantially identical semiconductor devices in the stack,the first semiconductor device is master enabled, while the remainder ofthe devices in the stack are slave enabled. Additionally, transmittersin the stack's slave circuit 248 communicate to receivers in the bottomdie's master circuit 246, while transmitters in the bottom die's mastercircuit 246 communicate to receivers in the stack's slave circuit 248.

Read signals should travel in opposite direction as the write signals.For example, a read signal originated from device 236(4) would travelfrom a read channel slave circuit 248 to the S1 pad of device 236(4),through the TSV's between pads S2 and S1 in devices 236(3) and 236(2),and through the TSV between pads M2 and M1 in device 236(1), to a readchannel master circuit 246, and output by I/O buffer 244 through the “MIn” pad of device 236(1).

FIG. 3 is a schematic cross-sectional side view (cross-hatching removedfor clarity) of another exemplary stacked semiconductor device assembly300. As shown, the second group of connection pads of the interfacesemiconductor device (bottommost first semiconductor device) 302 iselectrically connected (such as through “solder bumps” or “C4 bumps”) tothe substrate 312 of the stacked semiconductor device assembly 300. Thefourth group of connection pads of the first semiconductor device 302 isthen electrically coupled to the first group of connection pads of thesecond semiconductor device 304. The third group of connection pads ofthe second semiconductor device 304 is connected to the first group ofconnection pads of the third semiconductor device 306; the third groupof connection pads of the third semiconductor device 306 is connected tothe first group of connection pads of the fourth semiconductor device308; and the third group of connection pads of the fourth semiconductordevice 308 is connected to the first group of connection pads of thefifth semiconductor device 310. Overmolding 316 is them provided overthe entire stack of semiconductor devices to insulate and protect thesemiconductor devices. The stacked semiconductor device assembly mayconnect to other electronic circuitry via any suitable electricalconnections, such as micro-BGA balls 314.

The stacked semiconductor device assembly allows any number of identicalsemiconductor devices to be stacked one on top of the other. Offsettingthe bottom semiconductor device from the remainder of the semiconductordevices in the stack allows only the interface (or bottom) semiconductordevice to perform functional or electrical operations differently ascompared to the other semiconductor devices in the stack. For example,as shown in FIGS. 2B and 2C, only the connection pad on the interfacesemiconductor device is connected to ESD circuitry, where the ESDcircuitry on the remainder of the semiconductor devices is not used orneeded. In another example, as shown in FIG. 2D, the bottom die may actas a “stack Master”, buffering JO data to multiple “stack Slaves” whichare substantially identical but have disabled master JO portions.

As all of the semiconductor devices in the stack are connected to oneanother in series, in some embodiments, it is desirable to select aparticular semiconductor device for receiving the transmitted signal.Selecting the appropriate semiconductor device may be achieved using anysuitable a chip select mechanism. One such suitable chip selectmechanism is described in co-pending U.S. patent application Ser. No.11/402,393, which is hereby incorporated by reference in its entirety.

FIG. 4 is a schematic cross-sectional side view (cross-hatching removedfor clarity) of another exemplary stacked semiconductor device assembly400. This embodiment includes a stacked semiconductor device assemblyconnected to a circuit board 408. The stacked semiconductor deviceassembly 400 includes multiple stacks of semiconductor devices 402 and404. One of the stacks of semiconductor devices 402 may includesemiconductor devices that are offset in two opposing directions. Thestacked semiconductor device assembly 400 may also include othercircuitry 422 that is not stacked.

FIG. 5 is a plan view of another stacked semiconductor device assembly500. Unlike the stacked semiconductor device assembly 100 shown in FIG.1A, this stacked semiconductor device assembly 400 includes one or moresemiconductor devices that are offset from one another in more than onedimension. For example, the uppermost semiconductor device 102(2) isoffset from the bottommost semiconductor device 102(1) along both of theorthogonal axes Y and X.

FIG. 6 is a schematic of a computer system using a stacked memorysemiconductor device assembly 626. The system 600 includes a pluralityof components, such as at least one central processing unit (CPU) 602; apower source 606, such as a power transformer, power supply, orbatteries; input and/or output devices, such as a keyboard and mouse 610and a monitor 608; communication circuitry 612; a BIOS 620; a level two(L2) cache 622; Mass Storage (MS) 624, such as a hard-drive; RandomAccess Memory (RAM) 626; and at least one bus 614 that connects theaforementioned components. These components are at least partiallyhoused within a housing 616. Some components may be consolidatedtogether, such as the L2 cache 622 and the CPU 602. The RAM 626 includesone or more stacked semiconductor device assemblies 300 described above.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be understood that variousadditions, modifications and substitutions may be made therein withoutdeparting from the spirit and scope of the present invention as definedin the accompanying claims. In particular, it will be clear to thoseskilled in the art that the present invention may be embodied in otherspecific forms, structures, arrangements, proportions, and with otherelements, materials, and components, without departing from the spiritor essential characteristics thereof. The presently disclosedembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims, and not limited to the foregoingdescription.

What is claimed is:
 1. A stacked semiconductor device assemblycomprising: first and second substantially identical integrated circuit(IC) devices, each of the first and second IC devices including: firstinterface circuits each having a first capacitance; second interfacecircuits each having a second capacitance that is lower than the firstcapacitance; a first set of through vias coupled to respective ones ofthe first interface circuits; and a second set of through vias coupledto respective ones of the second interface circuits; and wherein thefirst and second IC devices are stacked one on top of another and offsetfrom each other such that the first set of through vias of the first ICdevice are aligned with and electrically connected to respective ones ofthe second set of through vias of the second IC device.
 2. The stackedsemiconductor device assembly of claim 1, wherein each of the first andsecond IC devices comprises core circuitry, wherein the stackedsemiconductor device assembly is configured to communicate data betweenthe core circuitry and the first interface circuits on the first ICdevice and to communicate data between the core circuitry and the secondinterface circuits on the second IC device.
 3. The stacked semiconductordevice assembly of claim 2, wherein the stacked semiconductor deviceassembly is further configured to communicate data between the corecircuitry of the second IC device and the first interface circuits ofthe first IC device.
 4. The stacked semiconductor device assembly ofclaim 1, wherein each of the first interface circuits on a respective ICdevice includes an I/O pad connected to electrostatic dischargecircuitry on the respective IC device.
 5. The stacked semiconductordevice assembly of claim 1, wherein each of the second interfacecircuits on a respective IC device includes an I/O pad that is notconnected to electrostatic discharge circuitry on the respective ICdevice.
 6. The stacked semiconductor device assembly of claim 1, whereinthe stacked semiconductor device assembly is a memory module.
 7. Thestacked semiconductor device assembly of claim 1, wherein the firstinterface circuits are a read channel master and the second interfacecircuits are a read channel slave.
 8. The stacked semiconductor deviceassembly of claim 1, wherein the first interface circuits are a writechannel master and the second interface circuits are a write channelslave.
 9. The stacked semiconductor device assembly of claim 1, whereineach IC device is configured to communicate data using either the firstinterface circuits or the second interface circuits depending on whetherthe first set of through vias or the second set of through vias arecoupled to an external signal line.
 10. The stacked semiconductor deviceassembly of claim 1, wherein each semiconductor device of thesemiconductor devices is configured to operate in a different modedepending on whether the first set of through vias or the second set ofthrough vias are coupled to an external signal line.
 11. The stackedsemiconductor device assembly of claim 1, wherein the stackedsemiconductor device assembly is a DRAM module.
 12. The stackedsemiconductor device assembly of claim 1, wherein the stackedsemiconductor device assembly includes multiple distinct groups ofstacked IC devices.
 13. The stacked semiconductor device assembly ofclaim 1, wherein at least one of the IC device is offset from at leastanother one of the multiple IC devices along two axes that areperpendicular to one another and that are substantially parallel withsubstantially planer sides of the IC devices.
 14. (canceled) 15.(canceled)
 16. A stacked semiconductor device assembly comprising: firstand second substantially identical semiconductor devices, each of thefirst and second semiconductor devices including: a first interfacecircuit having a first capacitance; a second interface circuit having asecond capacitance that is substantially lower than the firstcapacitance; a first set of through vias coupled to the first interfacecircuit; and a second set of through vias coupled to the secondinterface circuit; and wherein the first and second semiconductordevices are stacked one on top of another and offset from each othersuch that the first set of through vias of the first semiconductordevice are aligned with and electrically connected to respective ones ofthe second set of through vias of the second semiconductor device. 17.The stacked semiconductor device assembly of claim 16, wherein each ofthe first and second semiconductor devices comprises core circuitry,wherein the stacked semiconductor device assembly is configured tocommunicate data between the core circuitry and the first interfacecircuit on the first semiconductor device and to communicate databetween the core circuitry and the second interface circuit on thesecond semiconductor device.
 18. The stacked semiconductor deviceassembly of claim 17, wherein the stacked semiconductor device assemblyis further configured to communicate data between the core circuitry ofthe second semiconductor device and the first interface circuit of thefirst semiconductor device.
 19. The stacked semiconductor deviceassembly of claim 16, wherein each of the first interface circuit on arespective semiconductor device includes an I/O pad connected toelectrostatic discharge circuitry on the respective semiconductordevice.
 20. The stacked semiconductor device assembly of claim 16,wherein the second interface circuit on a respective semiconductordevice includes an I/O pad that is not connected to electrostaticdischarge circuitry on the respective semiconductor device.